Metal particles-dispersed composition and flip chip mounting process and bump-forming process using the same

ABSTRACT

A flip chip mounting process wherein a semiconductor chip and a circuit substrate are electrically interconnected. The process includes the steps of preparing a semiconductor chip on which a first plurality of electrodes are formed and a circuit substrate on which a second plurality of electrodes are formed; supplying a composition onto a surface of the circuit substrate, such surface being provided with second plurality of electrodes; bringing the semiconductor chip into contact with a surface of said composition such that the first plurality of electrodes are opposed to the second plurality of electrodes; and heating the circuit substrate, and thereby electrical connections including a metal component constituting the metal particles dispersed in the composition are formed between the first plurality of electrodes and the second plurality of electrodes. Also, a thermoset resin layer is formed between the semiconductor chip and the circuit substrate.

This application is a divisional of prior application Ser. No.11/885,562, which is the National Stage of International Application No.PCT/JP2006/304256, filed Mar. 6, 2006.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a composition in which metal particlesare dispersed (the composition is hereinafter referred to also as “metalparticles-dispersed composition”). In particular, the present inventionrelates to a metal particles-dispersed composition that is used forelectrically interconnecting a circuit substrate and a semiconductorchip, or a metal particles-dispersed composition that is used forforming bumps on electrodes of a circuit substrate. Furthermore, thepresent invention relates to a flip chip mounting process and abump-forming process using the metal particles-dispersed composition.

2. Description of the Related Art

In recent years, mobile electronic devices such as a cellar phone, anotebook-size personal computer, PDA and a digital video camera havebeen increasingly used, and they are becoming smaller, thinner andlighter. There has been also increasing a demand for a high performanceand a multifunction of the mobile electronic devices. As a result,electronic components such as a semiconductor device and a circuitcomponent are becoming ultrasmall, and thereby a mounting process or apackaging process of the electronic components has been improved. Also,a high-density process of an electronic circuit has been rapidlyimproved.

The technology needed for the high-density process of the electroniccircuit is a high-density mounting technology or a high-densitypackaging technology for a semiconductor integrated circuit (LSI). Witha rapid development of a high pin-number and a fine pitch for connectingelectrodes (which are hereinafter referred to also as “electrode(s)”) ofa LSI chip, semiconductor packaging technologies such as CSP (chip sizepackage) by performance of the flip chip mounting of a bare chip as wellas PPGA and BGA mounting processes for external terminals have beencommonly used. Therefore, there is a demand for a new mountingtechnology or a new packing technology that can accommodate a high-speedprocessing and a miniaturization of a mounted IC as well as a highnumber of input/output terminals of the mounted IC.

In a flip chip mounting process, firstly, a plurality of electrode padsare formed on a semiconductor chip. Then, bumps are formed on theelectrode pads by using a material such as a solder, Au or the like.Subsequently the semiconductor chip is mounted over a circuit substratesuch that the bumps of the semiconductor chip are opposed to a pluralityof electrodes formed on the circuit substrate. This results in aformation of an electrical conduction between the bumps and theelectrodes. After that, a resin material (underfill agent) is pouredinto a clearance gap between the semiconductor chip and the circuitsubstrate so as to form a mechanical connection between thesemiconductor chip and the circuit substrate.

For mounting a next-generation LSI having 5000 or more electrodes over acircuit substrate, it is required to form fine-pitch bumps with theirpitch of 100 μm or less. It is, however, difficult for a conventionalsolder bump-forming process to form such fine-pitch bumps.

Moreover, from a viewpoint that a large number of bumps must be formedaccording to the number of the electrodes, a high productivity isrequired for reducing a manufacturing cost by reducing mounting tacttime per chip.

There has been developed a plating process and a screen printing processas a conventional bump-forming process. The plating process is suitablefor achieving a fine pitch, but it is complicated and has to compromisethe productivity. The screen printing process, on the other hand, has ahigh productivity, but is not suitable for achieving the fine pitchsince a mask is used.

Recently, there has been proposed several processes for selectivelyforming solder bumps on electrodes of a LSI chip or a circuit substrate.These processes are not only suitable for achieving a fine pitch of thebumps, but also suitable for achieving a high productivity since aplurality of the fine bumps can be formed in a batch process.Accordingly they are expected as promising processes that can beapplicable to a mounting or packaging for the next-generation LSI.

According to one of these promising processes, a solder paste comprisinga mixture of solder powder and a flux is applied directly onto a wholesurface of a circuit substrate having electrodes (surfaces of theelectrodes have been oxidized). Subsequently the circuit substrate isheated so as to melt the solder powder. As a result, solder bumps(solder layers) are selectively formed on the electrodes without causingan electrical short circuit between the adjacent electrodes. SeeJapanese Patent Kokai Publication No. 2000-94179 (which is referred toalso as “patent literature 1”), for example.

According to another one of the promising processes, a paste composition(so-called “deposition type solder using chemical reaction”) mainlycomprising organic acid lead salt and tin metal is applied onto a wholesurface of a circuit substrate, the surface being provided withelectrodes. Subsequently the circuit substrate is heated so as to inducea displacement reaction for Pb and Sn, and thereby Pb/Sn alloy isselectively deposited on the electrodes of the circuit substrate. SeeJapanese Patent Kokai Publication No. H01-157796 (which is referred toalso as “patent literature 2”) and “Electronics Packaging Technology”,issued on September, 2000, pp. 38-45 (which is referred to also as“Non-patent literature 1”), for example.

There is also another process wherein bumps are selectively formed onelectrodes of a circuit substrate. In this process, the circuitsubstrate is immersed in a chemical solution so as to form an adhesivefilm only on surfaces of the electrodes of the circuit substrate. Then,solder powder is put into contact with the adhesive film so as to attachthe solder powder to the electrodes. See Japanese Patent KokaiPublication No. H07-74459 (which is referred to also as “patentliterature 3”), for example.

However, when the above-mentioned processes are employed, the flip chipmounting process requires the following steps (1) and (2) due to thefact that the bumps are formed on the electrode pads of thesemiconductor chip or on the electrodes of the circuit substrate:

(1) The step for forming an electrical connection between the opposedelectrodes by performance of a reflow process after the formation of thebumps and the mounting of the semiconductor chip over the circuitsubstrate; and

(2) The step for pouring an underfill resin into a clearance gap formedbetween the semiconductor chip and the circuit substrate so as to securethe semiconductor chip to the circuit substrate.

The steps (1) and (2) will cause an increase of the manufacturing cost.

Therefore, there is recently proposed another process. According to suchprocess, an electrical connection is formed at desired position bydisposing a film consisting of an anisotropic conductive material (whichcontains electrically-conductive particles) between a projectedelectrode of a semiconductor chip and an electrode of a circuitsubstrate, followed by heating and pressurizing the film. See JapanesePatent Kokai Publication No. 2000-332055 (which is referred to also as“patent literature 4”), for example.

There is also proposed another process wherein anelectrically-conductive adhesive consisting of a thermosetting resin andelectrically-conductive particles is supplied between a semiconductorchip and a circuit substrate, and thereafter the semiconductor chip ispressurized and the electrically-conductive adhesive is heated.According to this process, the molten electrically-conductive particlesare allowed to gather between electrodes of the semiconductor chip andelectrodes of the circuit substrate. As a result, an electricalconduction between each electrode of the semiconductor chip and eachelectrode of the circuit substrate is formed, and also a bonding betweenthe semiconductor chip and the circuit substrate is formed. See JapanesePatent Kokai Publication No. 2004-260131 (which is hereinafter referredto also as “patent literature 5”), for example.

SUMMARY OF THE INVENTION

In the technology disclosed in patent literature 5, a curing temperatureof the thermosetting resin is above a melting point of theelectrically-conductive particles. Despite, this, as a general rule, theviscosity of the supplied electrically-conductive adhesive graduallyincreases as a polymerization thereof proceeds (the polymerization beingbrought about by the heating). Therefore, a mobility of the meltedelectrically-conductive particles is impaired due to the viscosityincrease of the adhesive. As a result, there may be occurred a problemthat a part of the electrically-conductive particles is left outside ofthe region formed between each electrode of the semiconductor chip andeach electrode of the circuit substrate, which will lead to adeterioration of electrical insulating properties at the region locatedbetween the neighboring electrodes.

The present invention is directed to solve the above problem. That is tosay, an object of the present invention is to provide a composition thatcan solve a problem attributable to the viscosity increase. Also,another object of the present invention is to provide a satisfactoryflip chip mounting process and a satisfactory bump-forming process interms of a prevented short-circuit and thus in terms of a connectingreliability.

In order to solve the above problem, the present invention provides acomposition comprising a first component, a second component, metalparticles and a convection additive wherein

the metal particles are dispersed in the second component, and theconvection additive is contained in the second component;

the first component is contained in an interior of at least one of themetal particles, wherein the metal particles melt upon heating so thatthe first component comes in contact with the second component to form athermoset resin; and

the convection additive is capable of generating a gas upon heating.

It is preferred that the first component is a curing agent or a curingpromoter (accelerator) used for forming the thermoset resin, whereas thesecond component is a base resin used for forming the thermoset resin.

The composition of the present invention is at least characterized inthat the first component is built in at least one of the metal particlesthat are dispersed in the second component (i.e., at lease one of themetal particles dispersed in the second component has a built-in firstcomponent). Thus, a curing reaction between the first component and thesecond component is not initiated until the metal particles melt. Inother words, when a temperature reaches a melting point of the metalparticles, the curing reaction is initiated so that the viscosity of thecomposition increases. As a result, the viscosity of the composition iskept low during the starting phase of the heating (that is to say, “potlife” regarding the composition of the present invention is long).

The composition of the present invention is also characterized in thatthe convection additive is contained therein. When the convectionadditive is heated, it boils to generate a gas or it is decomposed togenerate a gas. Due to the movement of the generated gas, a convectioneffect is provided within the composition, which allows the movement ofthe metal particles. Thus, for example, in a case where the compositionof the present invention is supplied between a semiconductor chip and acircuit substrate in the flip chip mounting process, followed by beingheated, the metal particles can easily self-assemble into a regionbetween each electrode of the semiconductor chip and each electrode ofthe circuit substrate due to wettability of the electrodes (i.e., due tothe fact that the electrodes have high wettability to the metalparticles). As a result, electrical connections can be formed, each ofwhich serves to interconnect the opposed electrodes electrically. By theway, it is preferred that the convection additive is at least onematerial selected from the group consisting of xylene, isobutyl alcohol,isopentyl alcohol, butyl acetate, tetrachlorethylene, methyl isobutylketone, ethyl carbitol, butyl carbitol, ethylene glycol, aluminumhydroxide, dawsonite, ammonium metaborate, barium metaborate and sodiumhydrogen carbonate.

In a preferred embodiment, the curing agent is at least one materialselected from the group consisting of aliphatic amine, aromatic amine,aliphatic acid anhydride, cycloaliphatic acid anhydride, organicperoxide and polybasic acid; and

the base resin is at least one material selected from the groupconsisting of epoxy resin, unsaturated polyester resin, alkyd resin,polybutadiene resin, polyimide resin, polyamide resin and cyanate resin.

In a preferred embodiment, a metal component constituting the metalparticles is at least one alloy selected from the group consisting ofSn—Pb alloy, Sn—Ag alloy, Sn—Ag—Cu alloy, Sn—Bi—Ag—In alloy, Sn—Bi—Znalloy, Sn—Bi—Ag—Cu alloy, Sn—Zn alloy and Sn—Sb alloy.

It is preferred that the composition of the present invention is inpaste form or in sheet form. It is also preferred that a content of ametal component constituting the metal particles ranges from 0.5 to 30%by volume with respect to the composition.

In a preferred embodiment, a melting point of a metal componentconstituting the metal particles is between a curing reaction-initiatingtemperature and a peak temperature of the curing reaction with respectto a mixture of the first component and the second component. Similarly,in a preferred embodiment, a boiling point of the convection additive isbetween a curing reaction-initiating temperature and a peak temperatureof the curing reaction with respect to a mixture of the first componentand the second component. In another preferred embodiment, theconvection additive is decomposed to generate a gas under a temperaturecondition between a curing reaction-initiating temperature and a peaktemperature of the curing reaction with respect to a mixture of thefirst component and the second component.

The present invention also provides a flip chip mounting process usingthe above-mentioned composition. The flip chip mounting process of thepresent invention comprises the steps of:

(i) preparing a semiconductor chip on which a plurality of electrodes(a) (or “connecting terminals”) are formed and a circuit substrate onwhich a plurality of electrodes (b) (or “electrode terminals”) areformed (wherein the electrodes (a) and the electrodes (b) can be opposedto each other when the semiconductor chip is mounted over the circuitsubstrate);

(ii) supplying the composition of the present invention onto a surfaceof the circuit substrate, such surface being provided with theelectrodes (b);

(iii) bringing the semiconductor chip into contact with the suppliedcomposition such that the electrodes (a) of the semiconductor chip areopposed to the electrodes (b) of the circuit substrate; and

(iv) heating the circuit substrate, and thereby electrical connectionsconsisting of a metal component constituting the metal particles areformed between each electrode (a) and each electrode (b), and also athermoset resin layer is formed between the semiconductor chip and thecircuit substrate.

In this flip chip mounting process, the movement of the metal particlesand the molten metal component (i.e., the melted metal produced due tothe melting of the metal particles) is achieved due to the convectionphenomenon. As a result, the metal particles and the molten metalcomponent are allowed to self-assemble onto the electrodes (a) and/orthe electrodes (b), and thereby the electrical connection forinterconnecting each electrode (a) and each electrode (b) can be formed.In addition to that, the thermoset resin layer is formed between thesemiconductor chip and the circuit substrate through the contact of thefirst component and the second component, the contact being broughtabout by the melting of the metal particles. Therefore, the flip chipmounting process of the present invention can concurrently achieve“solder joint or solder connection” by use of the metal componentconstituting the metal particles and “formation of underfill resinlayer” by use of the thermoset resin.

Since the composition used for the flip chip mounting process of thepresent invention has a relatively long “pot life”, a stability of thecomposition at ambient temperatures (i.e., at ordinary temperatures) isimproved. Therefore, an operating efficiency upon performing the flipchip mounting process is significantly improved.

It is preferred that a plurality of the semiconductor chips are broughtinto contact with the supplied composition in the step(iii). The circuitsubstrate prepared in the step (i) may be a printed circuit board, aceramic substrate, a glass substrate or a semiconductor wafer.

The present invention also provides a process for forming bumps usingthe above-mentioned composition. The process for forming bumps of thepresent invention comprises the steps of:

(i) preparing a circuit substrate on which a plurality of electrodes (or“electrode terminals”) are formed, and also preparing a cover havingrelease properties;

(ii) supplying the composition of the present invention onto a surface(A) of the circuit substrate, such surface (A) being provided with theelectrodes;

(iii) bringing the cover into contact with the supplied composition;

(iv) heating the circuit substrate, and thereby bumps consisting of ametal component constituting the metal particles are formed on theelectrodes, and also a thermoset resin layer is formed between thecircuit substrate and the cover; and

(v) removing (or peeling away) the cover from the thermoset resin layer.

In the process for forming bumps of the present invention, the movementof the metal particles and the molten metal component (i.e., the meltedmetal produced due to the melting of the metal particles) is achieveddue to the convection phenomenon. As a result, the metal particles andthe molten metal component are allowed to self-assemble onto theelectrodes, and thereby the bumps can be formed. In addition to that,the thermoset resin layer is formed between the cover and the circuitsubstrate through the contact of the first component and the secondcomponent, the contact being brought about by the melting of the metalparticles.

The circuit substrate prepared in the step (i) may be a printed circuitboard, a ceramic substrate, a glass substrate or a semiconductor wafer.

According to the process for forming bumps of the present invention,bumps (solder bumps) having a high aspect ratio can be easily formed onthe circuit substrate. Moreover, according to the process for formingbumps of the present invention, fine-pitch bumps (fine-pitch solderbumps) can be also easily formed. The simplification of the bump-formingsteps can be achieved. Furthermore, the bump package region (except fora surface region on which the bumps are formed) is protected by thethermoset resin, which leads to an improvement of the reliability.

In a preferred embodiment of the process for forming bumps of thepresent invention,

between the step (i) and step (ii), a release agent layer is formed onthe surface (A) of the circuit substrate except for a surface regionprovided with the electrodes; and

in the step (v), not only the cover is removed from the thermoset resinlayer, but also the thermoset resin layer and the release agent layerare removed.

In a preferred embodiment of the process for forming bumps of thepresent invention,

a plurality of lands are formed on a surface (B) of the cover preparedin the step (i) such that a land pattern corresponds to that of theelectrodes of the circuit substrate, and also a release agent layer isformed on the surface (B) except for a surface region provided with thelands;

in the step the cover is brought into contact with the suppliedcomposition such that the lands of the cover are opposed to theelectrodes of the circuit substrate;

in the step (iv), the bumps consisting of the metal componentconstituting the metal particles (i.e., metal produced due to themelting of the metal particles) are formed so that the lands and theelectrodes are interconnected; and

in the step (v), the cover and the release agent layer are removedwhereas the lands are left to remain on the bumps.

In this embodiment, the bump package region except for a surface regionon which the bumps are formed is protected by the thermoset resin layer,which leads to an improvement of the connecting reliability. Also, theprojecting portion of each bump, which projects upward from the surfaceof the thermoset resin layer, can be used for a subsequent mountingprocess. Since the periphery of the bumps (except for the projectingportions of bumps) is surrounded by the thermoset resin, a fine pitch ofthe bumps can be achieved.

It is preferred that the cover prepared in the step (i) is the followingplate:

a plate made of glass;

a plate made of ceramic; or

a plate that is coated with a material having release properties withrespect to the thermoset resin, for example, coated with at least onematerial selected from the group consisting of silicone resin, fluorineresin (fluoroplastic), polypropylene resin, silicone oil, inorganicoxide, inorganic nitride and inorganic nitrided oxide. In this case, itis ensured that the cover is finally removed from the thermoset resinlayer.

Similarly, the release agent layer which may be formed between the step(i) and the step (ii) of the process for forming bumps is preferablymade of some material having release properties with respect to thethermoset so as to ensure a subsequent removal of the cover. Forexample, it is preferred that the release agent layer is formed byapplying at least one material selected from the group consisting ofsilicone resin, fluorine resin, polypropylene resin, silicone oil,inorganic oxide, inorganic nitride and inorganic nitrided oxide.

Furthermore, the present invention provides a semiconductor package thatis obtained by dividing the semiconductor wafer on which the bumps areformed by performance of the above process (i.e., the process forforming bumps of the present invention) into pieces. That is to say, achip size package (CSP) can be easily obtained by performance of theprocess for forming bumps of the present invention.

Due to the fact that the first component is built in at least one of themetal particles dispersed in the second component, the composition ofthe present invention provides an advantageous effect. In particular, ina case where the composition of the present invention is used for a flipchip mounting process or a process for forming bumps, the viscosity ofthe composition is kept low during the starting phase of the heatingsince a curing reaction between the first component and the secondcomponent is not initiated until the metal particles melt. As a result,the convection effect (which is occurred due to the convection additiveor a buoyant force based on the thermal motion) is not adverselyaffected during the starting phase of the heating, and thereby a smoothmovement of the metal particles can be performed within the composition.

Therefore, the following matters can be concluded:

-   -   According to the prior art wherein a pre-mixed composition of a        curing agent and a base resin for a thermoset resin (e.g., epoxy        resin) is used, the composition has a short “pot life”. As a        result, the curing reaction is already initiated and the        composition viscosity increases during the step of applying the        composition onto the circuit substrate or during the starting        phase of heating the circuit substrate, and thereby the        occurrence of the convection phenomenon may be suppressed so        that the self-assembly or the like of the metal particles is        adversely affected.    -   On the other hand, the present invention takes a long time        between a initiation of the heating and a completion of the        curing reaction since a curing reaction between the first        component and the second component is not initiated until the        metal particles melt. As a result, a satisfactory convection        effect is provided so that the self-assembly of the metal        particles is achieved wherein the metal particles are allowed to        move onto the electrodes or into a region between the opposed        electrodes.

As described above, in a case where the composition of the presentinvention is used for a flip chip mounting process or a process forforming bumps, the metal particles are allowed to efficientlyself-assemble onto the electrodes or into a region between the opposedelectrodes. It is thus possible to reduce a amount of the residual metalparticles that are left outside of electrodes or outside of the regionbetween the opposed electrodes, which will lead to a prevention of theshort-circuit. As a result, an excellent connecting reliability betweenthe opposed electrodes is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a cross-sectional view illustrating a metal particlecontained in a composition of the present invention, and particularly ametal particle having a metal layer and a core region in which a firstcomponent is contained.

FIG. 1B shows a cross-sectional view illustrating a metal particlecontained in a composition of the present invention, and particularly ametal particle having no first component and thus made of metal materialas a whole.

FIG. 1C shows a conceptual diagram of a DSC curve obtained from adifferential scanning calorimetry for a mixture of a first component anda second component.

FIG. 1D shows schematic views illustrating the steps in a process formanufacturing metal particles, each of which has a metal layer and acore region in which a first component is contained.

FIGS. 2A(a) to 2A(d) show cross-sectional views illustrating the stepsin a flip chip mounting process of the present invention according tothe first embodiment.

FIGS. 2B(a) to 2B(d) show cross-sectional views illustrating the stepsin a flip chip mounting process of the present invention according tothe first embodiment.

FIGS. 3A(a) to 3A(f) show cross-sectional views illustrating the stepsin a bump-forming process of the present invention according to thesecond embodiment.

FIGS. 3B(a) to 3B(f) show cross-sectional views illustrating the stepsin a bump-forming process of the present invention according to thesecond embodiment.

FIGS. 4( a) to 4(g) show cross-sectional views illustrating the steps ina bump-forming process of the present invention according to the thirdembodiment.

FIGS. 5( a) and 5(b) show a top plan view and a cross-sectional view(taken along the line A-A) illustrating a cover having releaseproperties that is used, for a bump-forming process of the presentinvention according to the fourth embodiment. FIG. 5( c) shows across-sectional view illustrating a circuit substrate that is preparedaccording to the cover.

FIGS. 6( a) to 6(f) show cross-sectional views illustrating the steps ina bump-forming process of the present invention according to the fourthembodiment.

FIG. 7 shows a cross-sectional view illustrating a modified example of acove having release properties that is used for a bump-forming processof the present invention according to the fourth embodiment.

FIGS. 8( a) to 8(d) show cross-sectional views illustrating the steps ina bump-forming process of the present invention according to the fifthembodiment.

FIG. 9 shows a cross-sectional view illustrating of a semiconductorpackage obtained by cutting a semiconductor wafer of FIG. 8( d) intodice.

FIGS. 10( a) to 10(d) show cross-sectional views illustrating the stepsin a bump-forming process of the present invention according to thesixth embodiment.

FIG. 11 shows a cross-sectional view illustrating of a semiconductorpackage obtained by cutting a semiconductor wafer of FIG. 10( d) intodice.

In the drawings, the reference numbers correspond to the followingelements:

-   1, 21, 31, 51: Metal particle having a metal layer and a core region    in which a first component is contained-   1′, 21′, 31′, 51′: Metal particle made of metal material (or solder    material) as a whole-   1″: Melted metal component (melted metal particle 1 and melted metal    layer 2)-   21″: Melted metal component (melted metal particle 21 and melted    metal layer 22)-   2, 22, 32, 52: Metal layer (solder material layer)-   20: Cylindrical metal member-   3 a, 23 a, 33 a, 53 a: First component-   3 b, 23 b, 33 b, 53 b: Second component-   3 c, 23 c, 33 c, 53 c: Thermoset resin or thermoset resin layer-   4, 24, 34, 54: Composition of the present invention (metal    particles-dispersed composition)-   5, 25: Electrode (Electrode (b)) of circuit substrate-   6, 26: Circuit substrate-   7: Electrode (Electrode (a)) of semiconductor chip-   8: Semiconductor chip-   9, 28, 36, 55: Gas generated from convection additive-   10: Connection (solder connection)-   27, 41, 63: Cover having release properties-   29, 58 Bump (solder bump)-   35, 43: Release agent layer-   42: Land-   56: Bump body-   57: Top of bump (projecting portion of bump)-   61: Electrode of semiconductor wafer-   62: Semiconductor wafer-   64: Dicing line-   65, 66: Semiconductor package

DETAILED DESCRIPTION OF THE INVENTION

With reference to the attached drawings, a few embodiments of thepresent invention will be hereinafter described. As to the drawings, theconstituent elements having substantially the same function carry thesame reference number for ease of the description.

(Metal Particles-Dispersed Composition)

A metal particles-dispersed composition of the present invention will bedescribed. The metal particles-dispersed composition comprises a firstcomponent, a second component, metal particles and a convectionadditive. The second component can serve as a continuous phase in whichthe metal particles are dispersed. The convection additive is containedin the second component so that a mixture of the convection additive andthe second component is formed. In a case where the convection additiveis in liquid form, the convection additive and the second componentserve as a continuous phase. In a case where the convection additive isin solid form or powder form, the convection additive is dispersed inthe second component. The first component is contained in an interior ofat least one of the metal particles.

(Metal Particles)

It is preferred that at least one of the metal particles has the firstcomponent in the core region thereof. In other words, the metalparticles are composed of metal particles 1 as shown in FIG. 1A andmetal particles 1′ as shown in FIG. 1B. In the metal particle 1 shown inFIG. 1A, the first component 3 a is covered with a metal layer 2. On theother hand, the metal particle 1′ shown in FIG. 1B consists of only ametal component. Since a thermoset resin is formed from the firstcomponent and the second component, the amount of the first component isdetermined depending on the amount of the thermoset resin to be formed.On the other hand, the amount of a metal component constituting themetal particles is determined depending on the amount of bumps orelectrical connections to be formed. Therefore, in some cases, all themetal particles contained in the composition may be metal particles 1.

In a case where a content of a metal component constituting the metalparticles 1,1′ is less than 0.5% by volume with respect to thecomposition, a satisfactory size of the connections formed between theopposed electrodes cannot be obtained in the flip chip mounting process,which may cause a poor electrical conduction. On the other hand, in acase where a content of a metal component constituting the metalparticles 1,1′ is more than 30% by volume with respect to thecomposition, this may increase the surplus metal particles that have notbeen used for the formation of the electrical connections and thus existas residual metal, which will cause a short-circuit at the regionbetween the neighboring connections. It is therefore preferred that acontent of a metal component constituting the metal particles 1,1′ranges from 0.5 to 30% by volume with respect to the composition.

As a metal component constituting the metal particles 1,1′ (i.e., acomponent constituting particles 1′ and metal layer 2), a conventionalsolder material such as Pb—Sn alloy may be used. Some solder materialsthat have been recently developed in terms of an environmental problemmay be also used. The examples of such solder materials include Sn—Agalloy, Sn—Ag—Cu alloy, Sn—Bi—Ag—In alloy, Sn—Bi—Zn alloy, Sn—Bi—Ag—Cualloy and Sn—Zn alloy. In a case where the metal component constitutingthe metal particles 1,1′ is solder material, the metal particles 1,1′can be referred to also as “solder particles”.

It is preferred that the metal component constituting the metalparticles 1,1′ has a melting point suitable for a flip chip mountingprocess and a bump-forming process. For example, it is preferred thatthe melting point of the metal component constituting the metalparticles 1,1′ is above a curing reaction-initiating temperature (T₀) ofa mixture of the first component and the second component. It is morepreferred that the melting point of the metal component constituting themetal particles 1,1′ is between the curing reaction-initiatingtemperature (T₀) and a peak temperature (T₁) of the curing reaction withrespect to the mixture of the first component and the second component.“Curing reaction-initiating temperature (T₀)” used herein is one asshown in FIG. 1C. Namely, in a DSC curve obtained from a differentialscanning calorimetry for a mixture of the first component and the secondcomponent, the curing reaction-initiating temperature (T₀) is atemperature at the intersection of a baseline and a tangent line passingthrough an inflection point P (such inflection point P being located ina curve section rising toward an exothermic peak). Similarly, the peaktemperature (T₁) of the curing reaction is a temperature at anexothermic peak in the DSC curve obtained from a differential scanningcalorimetry for a mixture of the first component and the secondcomponent. The term “differential scanning calorimetry” used herein is acalorimetry by using a differential scanning calorimeter (SeikoInstruments Inc., DSC220) wherein a mixture of the first component andthe second component charged in a sample pan (which is made of aluminum)is heated from a room temperature at a rise rate of 10° C./min.

(First Component)

The first component 3 a is preferably a curing agent or a curingpromoter used for forming a general thermoset resin. For example, it ispreferred that the first component 3 a is at least one kind of curingagent selected from the group consisting of aliphatic amine, aromaticamine, aliphatic acid anhydride, cycloaliphatic acid anhydride, organicperoxide and polybasic acid.

(Method for Producing Metal Particles)

Next, a method for producing metal particles 1 will be described. Thereis no limit on the method for producing metal particles 1 in the presentinvention. Any suitable methods can be employed as long as the firstcomponent is contained in an interior of each of particulate metals. Forexample, the following methods (1) and (2) can be employed:

(1) Method by Performance of Elongation Process

FIG. 1D shows schematic views illustrating a method for producing themetal particles 1 by performance of an elongation process. Firstly, asshown in FIG. 1D(a), a metal cylinder 20 in which the first component 3a is deposited is formed, followed by being elongated as shown in FIG.1D(b). These are performed by means of an extrusion die so as to form athin elongated metal member. Subsequently, a plurality of squeezed ordented portions of the metal member are formed at a desired spacing (seeFIG. 1D(c)), and thereafter the metal member is divided into pieces bycutting it at the squeezed or dented portions (see FIG. 1D(d)). Afterthat, a spheronization process is performed if needed. As a result, themetal particles 1 as shown in FIG. 1D(e) are obtained.

(2) Method by Performance of Embossing Process

Firstly, the first component is applied on a first metal plate, andthereafter a second metal plate is disposed on the supplied firstcomponent. Subsequently, the first metal plate and the second metalplate are welded with pressure by an embossing press machine, followedby cutting the welded plates into pieces. As a result, the metalparticles 1 are obtained.

(Second Component)

The second component may be any suitable ones as long as they arecapable of forming a thermoset resin through a contact with the firstcomponent. It is preferred that the second component is a base resinused for forming a general thermoset resin. For example, it is preferredthat the second component is a base resin used for forming at least onethermoset resin selected from the group consisting of epoxy resin,unsaturated polyester resin, alkyd resin, polybutadiene resin, polyimideresin, polyamide resin and cyanate resin. In a case where thecomposition having a paste form or a sheet form is desirable, the secondcomponent having higher viscosity is preferably used.

As described above, it is preferred that the first component is a curingagent or a curing promoter used for forming the thermoset resin whereasthe second component is a base resin used for forming the thermosetresin. However, it is also preferred that the first component is a baseresin used for forming the thermoset resin whereas the second componentis a curing agent or a curing promoter used for forming the thermosetresin.

Furthermore, the second component may be some material capable ofinitiating its curing process or promoting its curing process after themelting of the metal particles.

(Convection Additive Contained in Composition)

The convection additive may be any suitable ones as long as they canprovide a convection effect within the composition when being heated. Itis preferred that the convection additive boils so as to generate a gaswhen it is heated. It is also preferred that the convection additive isdecomposed to generate or release a gas when it is heated. For example,the convection additive is preferably at least one material selectedfrom the group consisting of xylene, isobutyl alcohol, isopentylalcohol, butyl acetate, tetrachlorethylene, methyl isobutyl ketone,ethyl carbitol, butyl carbitol, ethylene glycol, aluminum hydroxide,dawsonite, ammonium metaborate, barium metaborate and sodium hydrogencarbonate.

It is preferred that convection additive has physical propertiessuitable for a flip chip mounting process and a bump-forming process.For example, it is preferred that a boiling point of the convectionadditive is between a curing reaction-initiating temperature (T₀) and apeak temperature (T₁) of the curing reaction of a mixture of the firstcomponent and the second component. It is also preferred that theconvection additive is decomposed to generate gas at a temperaturecondition of between the curing reaction-initiating temperature (T₀) andthe peak temperature (T₁) of a curing reaction with respect to a mixtureof the first component and the second component. As described above,“curing reaction-initiating temperature (T₀)” used herein is one asshown in FIG. 1C. Namely, in a DSC curve obtained from a differentialscanning calorimetry for a mixture of the first component and the secondcomponent, the curing reaction-initiating temperature (T₀) is atemperature at the intersection of a baseline and a tangent line passingthrough an inflection point P (such inflection point P being located ina curve section rising toward an exothermic peak). Similarly, the peaktemperature (T₁) of the curing reaction is a temperature at anexothermic peak in the DSC curve obtained from a differential scanningcalorimetry for a mixture of the first component and the secondcomponent. The term “differential scanning calorimetry” used herein is acalorimetry by using a differential scanning calorimeter (SeikoInstruments Inc., DSC220) wherein a mixture of the first component andthe second component charged in a sample pan (which is made of aluminum)is heated from a room temperature at a rise rate of 10° C./min.

The First Embodiment

With reference to FIGS. 2A(a) to 2A(d), a flip chip mounting processusing a composition of the present invention according to the firstembodiment will be hereinafter described. FIG. 2A shows cross-sectionalviews illustrating the steps in the flip chip mounting process of thepresent invention according to the first embodiment. In the drawings,double circle (⊚) indicates a metal particle 1 having a metal layer 2and a core region in which the first component 3 a is contained, whereassingle circle (◯) indicates a metal particle 1′ made of only the metalcomponent, and thus having no content of the first component. It shouldbe noted that the convection additive is not shown in the drawings.

In this first embodiment, the following materials are used. As a metalcomponent constituting the metal particles 1′ and the metal layer 2, asolder material consisting of Sn—Ag—Cu alloy is used. As a firstcomponent 3 a, dicyandiamide (curing agent) is used. As a secondcomponent 3 b, bisphenol A type epoxy resin (base resin) is used. As aconvection additive, butyl acetate is used.

Firstly, as shown in FIG. 2A(a), a metal particles-dispersed composition4 of the present invention is applied onto a surface of a circuitsubstrate 6, the surface being provided with a plurality of electrodes 5(i.e., electrodes (b)). Subsequently, a semiconductor chip 8 which isprovided with a plurality of electrodes 7 (i.e., electrodes (a)) isbrought into contact with a surface of the supplied composition 4. Inthis regard, the semiconductor chip 8 is mounted over the circuitsubstrate 6 such that the electrodes 7 of the semiconductor chip 8 areopposed to the electrodes 5 of the circuit substrate 6.

Subsequently, as shown in FIG. 2A(b), the circuit substrate 6 is heated.As the temperature rises, the viscosity of the second component 3 bbecomes lower. This allows the movement of the metal particles 1,1′.Furthermore, as the temperature rises, the convection additive (butylcarbitol) boils to generate a gas 9. The generated gas 9 provides aconvection effect (as indicated as an arrow A in FIG. 2A) within thecomposition until the gas 9 escapes to the outside. This convectioneffect makes it possible to promote a movement of the metal particles1,1′.

The moving metal particles 1,1′ are allowed to self-assemble into aregion between each electrode 7 of the semiconductor chip 8 and eachelectrode 5 of the circuit substrate 6 as shown in FIG. 2A(c) due tohigh wettability of the electrodes 5 and 7.

A metal component constituting the metal particles 1,1′ melts as thetemperature rises. The melted metal component agglomerates and grows soas to interconnect each electrode 7 of the semiconductor chip 8 and eachelectrode 5 of the circuit substrate 6. The melting of the metalcomponent causes the melting of the metal layer 2 of the metal particle1. Thus, the first component 3 a (dicyandiamide) that has been containedin the metal particles 1 is released into the second component 3 b.(bisphenol A type epoxy resin), which leads to a contact of the firstcomponent 3 a and the second component 3 b. This contact initiates acuring reaction between the first component 3 a and the second component3 b, and thereby a thermoset resin 3 c is formed. The formation of thethermoset resin 3 c causes a viscosity rise of the composition 4. Thismeans that the viscosity of the composition 4 is kept low while themetal particles 1,1′ are moving since the curing reaction is not yetinitiated during the starting phase of the heating. As a result, theself-assembling of the metal particles 1,1′ is not adversely affectedduring the starting phase of the heating.

The sufficient growth of the melted metal component between eachelectrode 7 of the semiconductor chip 8 and each electrode 5 of thecircuit substrate 6 results in a formation of the connection 10 whichinterconnects each electrode 7 of the semiconductor chip 8 and eachelectrode 5 of the circuit substrate 6, as shown in FIG. 2A(d). Also,the completion of the curing reaction between the first component 3 aand the second component 3 b results in a formation of a thermoset resinlayer 3 c located between the circuit substrate 6 and the semiconductorchip 8, and thereby the semiconductor chip 8 is mechanically secured tothe circuit substrate 6.

In this way, the flip chip mounting process of the present inventionaccording to the first embodiment can concurrently achieve “solder jointor solder connection” by use of the metal component and “formation ofunderfill resin” by use of the thermoset resin.

According to the first embodiment, prior to the melting of the metalparticles 1,1′, the metal particles 1,1′ self-assemble into a regionbetween each electrode 7 of the semiconductor chip 8 and each electrode5 of the circuit substrate 6. In this regard, however, the metalparticles 1,1′ may melt while they are moving (see FIGS. 2B(a) to 2B(d),particularly FIG. 2B(c)) as long as the self-assembly of the metalparticles 1,1′ is not adversely affected. In this case, themovement/self-assembly of the metal particles 1,1′ and a molten metalcomponent is performed at the same time when the curing reaction betweenthe first component and the second component proceeds.

The Second Embodiment

With reference to FIGS. 3A(a) to 3A(f), a process for forming bumpsusing a composition of the present invention according to the secondembodiment will be hereinafter described. FIGS. 3A(a) to 3A(f) showcross-sectional views illustrating the steps in the process for formingbumps of the present invention according to the second embodiment.

In the second embodiment, the following materials are used. As a metalcomponent constituting the metal particles 21′ and the metal layer 22, asolder material consisting of Pb—Sn alloy is used. As a first component23 a, a chain aliphatic amine, e.g., ethylenediamine (curing agent) isused. As a second component 23 b, bisphenol F type epoxy resin (baseresin) is used. As a convection additive, a liquid mixture of butylcarbitol and isobutyl alcohol is used.

Firstly, as shown in FIG. 3A(a), a metal particles-dispersed composition24 of the present invention is applied onto a surface (surface (A)) of acircuit substrate 26, the surface (surface (A)) being provided with aplurality of electrodes 25.

Subsequently, as shown in FIG. 3A(b), a cover 27 having releaseproperties is brought into contact with a surface of the suppliedcomposition 24. In this regard, the cover 27 having release propertiesis a plate made of polypropylene resin or the like.

Next, as shown in FIG. 3A(c), the circuit substrate 26 is heated. As thetemperature rises, the viscosity of the second component 23 b (bisphenolF type epoxy resin) becomes lower. This allows the movement of the metalparticles 21,21′. Furthermore, as the temperature rises, the convectionadditive (liquid mixture of butyl carbitol and isobutyl alcohol) boilsto generate a gas 28. The generated gas 28 provides a convection effect(as indicated as an arrow A in FIG. 3A) within the composition until thegas 28 escapes to the outside. This convection effect makes it possibleto promote a movement of the metal particles 21,21′.

The moving metal particles 21,21′ are allowed to self-assemble onto asurface of each electrode 25 of the circuit substrate 26 as shown inFIG. 3A(d) due to high wettability of the electrodes 25.

A metal component constituting the metal particles 21,21′ melts as thetemperature rises. The melted metal component agglomerates and growstoward a surface of the cover 27 from a surface of each electrode 25.The melting of the metal component causes the melting of the metal layer22 of the metal particle 21. Thus, the first component 23 a(ethylenediamine) that has been contained in the metal particles 21 isreleased into the second component 23 b (bisphenol F type epoxy resin),which leads to a contact of the first component 23 a and the secondcomponent 23 b. This contact imitates a curing reaction between thefirst component 23 a and the second component 23 b, and thereby athermoset resin 23 c is formed. The formation of the thermoset resin 23c causes a viscosity rise of the composition 24. This means that theviscosity of the composition 24 is kept low while the metal particles21,21′ are moving since the curing reaction is not yet initiated duringthe starting phase of the heating. As a result, the self-assembling ofthe metal particles 21,21′ is not adversely affected during the startingphase of the heating. In other words, the melted metal component hasalready been growing from the surface of each electrode 25 by the timethe curing reaction between the first component and the second componentproceeds.

The sufficient growth of the melted metal component, which has grownfrom the surface of each electrode 25 to a surface of the cover 27,results in a formation of the bumps (solder bumps) 29, as shown in FIG.3A(e). Also, the completion of the curing reaction between the firstcomponent 23 a and the second component 23 b results in a formation of athermoset resin layer 23 c located between the circuit substrate 26 andthe cover 27.

Subsequently, the cover 27 is, removed (or peeled away) from thethermoset resin layer 23 c. Since the cover 23 c is a plate made ofpolypropylene resin or the like which has no adhesiveness to a thermosetresin, the cover 27 can be easily removed from the thermoset resin layer23 c. As a result, the circuit board 26 on which the bumps (solderbumps) 29 are formed can be obtained, as shown in FIG. 3A(f).

In a case where a semiconductor chip is flip chip connected to theobtained circuit substrate 26, the thermoset resin layer 23 c may beremoved from the circuit substrate 26 prior to the flip chip connection(not shown).

According to the second embodiment, prior to the melting of the metalparticles 21,21′, the metal particles 21,21′ self-assemble onto eachelectrode 25 of the circuit substrate 26. In this regard, however, themetal particles 21,21′ may melt while they are moving (see FIGS. 3B(a)to 3B(f), particularly FIG. 3B(d)) as long as the self-assembly of themetal particles 21,21′ is not adversely affected. In this case, themovement/self-assembly of the metal particles 21,21′ and a molten metalcomponent is performed at the same time when the curing reaction betweenthe first component and the second component proceeds.

The Third Embodiment

With reference to FIGS. 4( a) to 4(g), a process for forming bumps ofthe present invention using a composition of the present inventionaccording to the third embodiment will be hereinafter described. FIGS.4( a) to 4(g) show cross-sectional views illustrating the steps in theprocess for forming bumps of the present invention according to thethird embodiment.

In the third embodiment, the following materials are used. As a metalcomponent constituting the metal particles 31′ and the metal layer 32, asolder material consisting of Pb—Sn alloy is used. As a first component33 a, phthalic anhydride is used. As a second component 33 b,glycerin-based compound is used. As a convection additive, ammoniummetaborate is used.

Firstly, by performance of a coating method using a release agent (e.g.,silicone oil), a release agent layer 35 is formed on a surface (surface(A)) of a circuit substrate 26 except for a surface region provided withthe electrodes 25 (see FIG. 4( a)). Subsequently, a metalparticles-dispersed composition 34 of the present invention is appliedonto each electrode 25 and the release agent layer 35.

Next, as shown in FIG. 4( b), a cover 27 having release properties isbrought into contact with a surface of the supplied composition 34. Inthis regard, such cover 27 having release properties is a plate made ofsilicone resin or the like.

Next, as shown in FIG. 4( c), the circuit substrate 26 is heated. As thetemperature rises, the viscosity of the second component 33 b(glycerin-based compound) becomes lower. This allows the movement of themetal particles 31,31′. Furthermore, as the temperature rises, theconvection additive (ammonium metaborate) is decomposed to generate agas 36. The generated gas 36 provides a convection effect (as indicatedas an arrow A in FIG. 4) within the composition consisting primarily ofthe second component 33 b until the gas 36 escapes to the outside. Thisconvection effect makes it possible to promote a movement of the metalparticles 31,31′.

The moving metal particles 31,31′ are allowed to self-assemble onto eachelectrode 25 of the circuit substrate 26 as shown in FIG. 4( d) due tohigh wettability of the electrodes 25.

A metal component constituting the metal particles 31,31′ melts as thetemperature rises. The melted metal component agglomerates and growstoward a surface of the cover 27 from a surface of each electrode 25.The melting of the metal component causes the melting of the metal layer32 of the metal particle 31. Thus, the first component 33 a (phthalicanhydride) that has been contained in the metal particles 31 is releasedinto the second component 33 b (glycerin-based compound), which leads toa contact of the first component 33 a and the second component 33 b.This contact initiates a curing reaction between the first component 33a and the second component 33 b, and thereby a thermoset resin 33 c isformed. The formation of the thermoset resin 33 c causes a viscosityrise of the composition 34. This means that the viscosity of thecomposition 34 is kept low while the metal particles 31,31′ are movingsince the curing reaction is not yet initiated during the starting phaseof the heating. As a result, the self-assembling of the metal particles31,31′ is not adversely affected during the starting phase of theheating. In other words, the melted metal component has already beengrowing from the surface of each electrode 25 by the time the curingreaction between the first component and the second component proceeds.

The sufficient growth of the melted metal component, which has grownfrom the surface of each electrode 25, results in a formation of thebumps (solder bumps) 29, as shown in FIG. 4( e). Also, the completion ofthe curing reaction and the subsequent cooling of the resultingthermoset resin result in a formation of a thermoset resin layer 33 clocated between the circuit substrate 26 and the cover 27.

Subsequently, the cover 27 is removed (or peeled away) from thethermoset resin layer 33 c as shown in FIG. 4( f), and thereafter thethermoset resin layer 33 c and the release agent layer 35 are removed.As a result, the circuit board 26 on which the bumps 29 are left toremain can be obtained, as shown in FIG. 4( g).

The Fourth Embodiment

FIGS. 5( a) and 5(b) show a top plan view and a cross-sectional viewillustrating a cover 41 having release properties that is used for aprocess for forming bumps of the present invention according to thefourth embodiment. FIG. 5( b) shows the cross-sectional view of thecover 41 taken along the line A-A of FIG. 5( a). FIG. 5( c) shows across-sectional view illustrating the circuit substrate 26 that isprepared according to the cover 41. FIG. 6 shows cross-sectional viewsillustrating the main steps in the process for forming bumps of thepresent invention according to the fourth embodiment.

In the fourth embodiment, the following materials are used. As a metalcomponent constituting the metal particles 51′ and the metal layer 52, asolder material consisting of Sn—Zn alloy is used. As a first component53 a, benzoyl peroxide is used. As a second component 53 b, a mixture ofglycol, maleic anhydride and tertiary amine (curing promoter) is used.As a convection additive, sodium hydrogen carbonate is used.

As shown in FIGS. 5( a) and 5(b), lands 42 consisting primarily ofcopper(Cu) and/or tin(Sn) are formed on a surface (B) of the coveraccording to a configuration of a plurality of electrodes 25 of acircuit substrate 26 (such configuration of the electrodes 25 of thecircuit substrate 26 is shown in FIG. 5( c) in this case). Also, byperformance of a coating method, a release agent layer 43 is formed onthe surface (B) of the cover 41 except for a surface region providedwith the lands 42. Such release agent layer consists primarily of epoxyresin that has no adhesiveness to a thermoset resin.

Firstly, as shown in FIG. 6( a), a metal particles-dispersed composition54 is applied onto a surface (surface (A)) of the circuit substrate 26,the surface (surface (A)) being provided with the electrodes 25.

Subsequently, as shown in FIG. 6( b), the cover 27 having lands 42 andthe release agent layer 43 formed thereon is brought into contact with asurface of the supplied composition 54. In this case, the cover 41 ismounted over the circuit substrate 26 such that each land 42 of thecover 41 is opposed to each electrode 25 of the circuit substrate 26.

Next, as shown in FIG. 6( c), the circuit substrate 26 is heated. As thetemperature rises, the viscosity of the second component 53 b becomeslower. This allows the movement of the metal particles 51,51′.Furthermore, as the temperature rises, the convection additive (sodiumhydrogen carbonate) is decomposed to generate a gas 55. The generatedgas 55 provides a convection effect (as indicated as an arrow A in FIG.6) within the composition until the gas 55 escapes to the outside. Thisconvection effect makes it possible to promote a movement of the metalparticles 51,51′.

The moving metal particles 51,51′ are allowed to self-assemble into aregion between each electrode 25 and each land 42 as shown in FIG. 6( d)due to high wettability of the electrode 25 and the land 42.

A metal component constituting the metal particles 51,51′ melts as thetemperature rises. The melted metal component agglomerates and grows soas to interconnect each electrode 25 and each land 42. The melting ofthe metal component causes the melting of the metal layer 52 of themetal particle 51. Thus, the first component 53 a (benzoyl peroxide)that has been contained in the metal particles 51 is released into thesecond component 53 b (mixture of glycol, maleic anhydride and tertiaryamine), which leads to a contact of the first component 53 a and thesecond component 53 b. This contact initiates a curing reaction betweenthe first component 53 a and the second component 53 b, and thereby athermoset resin 53 c is formed.

The sufficient growth of the melted metal component between eachelectrode 25 and each land 42 results in a formation of a bump body 56which electrically interconnects each electrode 25 and each land 42, asshown in FIG. 6( e). Also, the completion of the curing reaction betweenthe first component 53 a and the second component 53 b results in aformation of a thermoset resin layer 53 c located between the circuitsubstrate 26 and the cover 41.

After the thermoset resin layer 53 c is formed, the cover 41 and therelease agent layer 43 are removed (or peeled away) from the thermosetresin layer 53 c. In this regard, when the cover 41 and the releaseagent layer 43 are removed while each bump body 56 is still in moltenstate, the lands 42 are left to remain on each bump body 56. As aresult, there is provided bumps 58 (solder bumps) that respectively haveprojecting portions 57 with uniform height, such portions 57 beingprojected from a surface of the thermoset resin layer 53 c.

In a case where the resulting circuit substrate having the bumps 58 aresubsequently used for a flip chip mounting process using a semiconductorchip, the thermoset resin layer 53 c can serving as a “member forregulating a connecting distance”, which will lead to an achievement ofa satisfactory flip chip mounting process in terms of an excellentconnecting reliability.

In a case where a thickness of each land 42 formed on the cover 41 isapproximately equal to a thickness of the release agent layer 43 formedon the cover 41 as shown in FIG. 5( b), the thermoset resin ispreferably selected so as to occur a large volume shrinkage thereofduring the curing process of forming the thermoset resin layer 53 c.

As shown in FIG. 7, the release agent layer 43 may be thicker than thelands 42, in which case the higher projecting portions 57 of the bumps58 can be formed.

According to the fourth embodiment, as the thermoset resin, anunsaturated polyester resin is formed from the composition comprisingthe first component and the second component. In this regard, however,an epoxy resin may be formed from the composition. Even in this case,the bumps can be similarly formed.

The Fifth Embodiment

By performance of the process for forming bumps according to the fifthembodiment, not only bumps can be formed on electrodes provided in acircuit element of a semiconductor wafer, but also a region of thecircuit element except for a bumps-formed surface can be protected witha resin layer. The process for forming bumps according to the fifthembodiment can achieve a formation of a chip size package (CSP). Withreference to FIGS. 8 and 9, the process for forming bumps of the presentinvention according to the fifth embodiment will be described in detail.

FIG. 8 shows cross-sectional views illustrating the main steps in theprocess for forming bumps according to the fifth embodiment. FIG. 9shows a cross-sectional view illustrating of a semiconductor packageobtained from a semiconductor wafer of FIG. 8( d).

A metal particles-dispersed composition used in the fifth embodiment isthe same as the composition 24 used in the second embodiment.

Firstly, as shown in FIG. 8( a), the metal particles-dispersedcomposition 24 is applied onto a surface of a semiconductor wafer 62,the surface being provided with electrodes 61. In this regard, however,the metal particles-dispersed composition 24 is applied only ontoelectrodes-formed surface regions (i.e., surface regions on which theelectrodes 61 are formed) and adjacent surface regions thereof.

Subsequently, as shown in FIG. 8( b), a cover 63 having releaseproperties (i.e., a plate made of polypropylene resin or the like) isbrought into contact with a surface of the supplied composition 24. Itis preferred that the size of the cover 63 is approximately the same asthat of the semiconductor wafer 62. However, it may be possible to use aplurality of covers 63, each of which has the size of the corresponding“circuit element area” of the semiconductor wafer.

Next, as in the case of the second embodiment, bumps (solder bumps) 29are formed on the electrodes 61 by performing the heating step (see FIG.8( c)). After that, the cover 63 is removed (see FIG. 8( d)).

Subsequently, the semiconductor wafer is cut into dice along the line 64(i.e., dicing line 64). As a result, a semiconductor package 65 having achip size can be obtained as shown in FIG. 9. When the semiconductorpackage 65 is mounted over a circuit substrate or the like byperformance of a conventional flip chip mounting process, an electroniccircuit substrate whose size is smaller than ever before can beobtained.

It will be understood that the cover 41 of the fourth embodiment can beused as the cover 63 of this fifth embodiment.

The Sixth Embodiment

The sixth embodiment is one wherein the fifth embodiment is modified.FIG. 10 shows cross-sectional views illustrating the main steps in aprocess for forming bumps according to the sixth embodiment. FIG. 11shows a cross-sectional view illustrating of a semiconductor packageobtained from a semiconductor wafer of FIG. 10( d).

Although the metal particles-dispersed composition 24 is applied onlyonto the limited region (i.e., electrodes 61-formed surface regions andthe adjacent surface regions thereof) in the fifth embodiment, thecomposition 24 is applied onto an approximately entire surface region ofa semiconductor wafer as shown in FIG. 10( d) in the sixth embodiment.It will be noted that there is no limit on the surface region forapplying the metal particles-dispersed composition 24 as long as all theelectrodes 61 are covered with the applied composition 24.

The obtained semiconductor wafer is preferably cut into dice along thedicing line 64 shown in FIG. 10( d), in which case the semiconductorpackage 66 having a chip size can be obtained as shown in FIG. 11.

The present invention has been hereinabove described according to someembodiments. It will be however understood by those skilled in the artthat the present invention is not limited to such embodiments and can bemodified in various ways.

For example, instead of applying the metal particles-dispersedcomposition having a paste form onto the circuit substrate, the metalparticles-dispersed composition that is preliminarily semi-cured andthus has a sheet form may be interposed between the circuit substrateand the semiconductor chip. Moreover, in a case where a curing reactionbetween the curing agent and the base resin proceeds relativelymoderately, a mixture of the curing agent and the base resin may be usedas the first component whereas the curing promoter may be used as thesecond component. In this case, the curing reaction will proceed rapidlywhen the first component comes in contact with the second component,such contact being brought about by the melting of the metal particles.

The present invention as described above includes the following aspects:

The first aspect: A composition comprising a first component, a secondcomponent, metal particles and a convection additive

wherein

said metal particles are dispersed in said second component, and saidconvection additive is contained in said second component;

said first component is contained in an interior of at least one of themetal particles, wherein said metal particles melt upon heating so thatsaid first component comes in contact with said second component to forma thermoset resin; and

said convection additive is capable of generating a gas upon heating

The second aspect: The composition according to the first aspect,wherein said first component is a curing agent or a curing promoter usedfor forming said thermoset resin, whereas said second component is abase resin used for forming said thermoset resin.

The third aspect: The composition according to the second aspect,wherein

said curing agent is at least one material selected from the groupconsisting of aliphatic amine, aromatic amine, aliphatic acid anhydride,cycloaliphatic acid anhydride, organic peroxide and polybasic acid; and

said base resin is at least one material selected from the groupconsisting of epoxy resin, unsaturated polyester resin, alkyd resin,polybutadiene resin, polyimide resin, polyamide resin and cyanate resin.

The fourth aspect: The composition according to any one of the first tothe third aspects, wherein a metal component constituting said metalparticles is at least one alloy selected from the group consisting ofSn—Pb alloy, Sn—Ag alloy, Sn—Ag—Cu alloy, Sn—B—Ag—In alloy, Sn—Bi—Znalloy, Sn—Bi—Ag—Cu alloy, Sn—Zn alloy and Sn—Sb alloy.

The fifth aspect: The composition according to any one of the first tothe fourth aspects, wherein

said convection additive is at least one material selected from thegroup consisting of xylene, isobutyl alcohol, isopentyl alcohol, butylacetate, tetrachlorethylene, methyl isobutyl ketone, ethyl carbitol,butyl carbitol, ethylene glycol, aluminum hydroxide, dawsonite, ammoniummetaborate, barium metaborate and sodium hydrogen carbonate.

The sixth aspect: The composition according to any one of the first tothe fifth aspects, wherein said gas provides a convection effect withinsaid composition.

The seventh aspect: The composition according to any one of the first tosixth aspects, wherein said composition is in paste form or in sheetform.

The eighth aspect: The composition according to any one of the first tothe seventh aspects, wherein a content of a metal component constitutingsaid metal particles ranges from 0.5 to 30% by volume with respect tosaid composition.

The ninth aspect: The composition according to any one of the first tothe eighth aspects, wherein

a melting point of a metal component constituting said metal particlesis between a curing reaction-initiating temperature and a peaktemperature of the curing reaction with respect to a mixture of saidfirst component and said second component.

The tenth aspect: The composition according to any one of the first tothe ninth aspects, wherein

a boiling point of said convection additive is between a curingreaction-initiating temperature and a peak temperature of the curingreaction with respect to a mixture of said first component and saidsecond component, or

said convection additive is decomposed to generate a gas under atemperature condition between a curing reaction-initiating temperatureand a peak temperature of said curing reaction with respect to a mixtureof said first component and said second component.

The eleventh aspect: A flip chip mounting process wherein asemiconductor chip and a circuit substrate are electricallyinterconnected, said process comprising the steps of:

(i) preparing a semiconductor chip on which a plurality of electrodes(a) are formed and a circuit substrate on which a plurality ofelectrodes (b) are formed;

(ii) supplying the composition according to any one of the first to thetenth aspects onto a surface of said circuit substrate, such surfacebeing provided with said electrodes (b);

(iii) bringing said semiconductor chip into contact with a surface ofsaid composition such that said electrodes (a) of said semiconductorchip are opposed to said electrodes (b) of said circuit substrate; and

(iv) heating said circuit substrate, and thereby electrical connectionsconsisting of a metal component constituting said metal particles areformed between said electrodes (a) and said electrodes (b), and also athermoset resin layer is formed between said semiconductor chip and saidcircuit substrate.

The twelfth aspect: The flip chip mounting process according to theeleventh aspect, wherein a plurality of said semiconductor chips arebrought into contact with said surface of said composition in the step(iii).

The thirteenth aspect: The flip chip mounting process according to theeleventh or the twelfth aspect, wherein said circuit substrate preparedin the step (i) is a printed circuit board, a ceramic substrate, a glasssubstrate or a semiconductor wafer.

The fourteenth aspect: A process for forming bumps on a plurality ofelectrodes of a circuit substrate, comprising the steps of:

(i) preparing a circuit substrate on which a plurality of electrodes areformed, and also a cover having release properties;

(ii) supplying the composition according to any one of the first to thetenth aspects onto a surface (A) of said circuit substrate, such surface(A) being provided with said electrodes;

(iii) bringing said cover into contact with a surface of saidcomposition;

(iv) heating said circuit substrate, and thereby bumps consisting of ametal component constituting said metal particles are formed on saidelectrodes, and also a thermoset resin layer is formed between saidcircuit substrate and said cover; and

(v) removing said cover.

The fifteenth aspect: The process according to the fourteenth aspect,wherein,

between the step (i) and step (ii), a release agent layer is formed onsaid surface (A) of said circuit substrate except for a surface regionprovided with said electrodes; and

in the step (v), not only said cover is removed, but also said thermosetresin layer and said release agent layer are removed.

The sixteenth aspect: The process according to the fourteenth aspect,wherein,

a plurality of lands are formed on a surface (B) of said cover preparedin the step (i) such that a land pattern corresponds to that of saidelectrodes of said circuit substrate, and also a release agent layer isformed on said surface (B) except for a surface region provided withsaid lands;

in the step (iii), said cover is brought into contact with the surfaceof said composition such that said lands of said cover are opposed tosaid electrodes of said circuit substrate;

in the step (iv), said bumps consisting of said metal componentconstituting said metal particles are formed so that said lands and saidelectrodes are interconnected; and

in the step (v), said cover and said release agent layer are removedwhereas said lands are left to remain on said bumps.

The seventeenth aspect: The process according to any one of thefourteenth to the sixteenth aspects, wherein said circuit substrateprepared in the step (i) is a printed circuit board, a ceramicsubstrate, a glass substrate or a semiconductor wafer.

The eighteenth aspect: The process according to any one of thefourteenth to the seventeenth aspects, wherein said cover prepared inthe step (i) is the following plate:

a plate made of glass;

a plate made of ceramic; or

a plate that is coated with at least one material selected from thegroup consisting of silicone resin, fluorine resin, polypropylene resin,silicone oil, inorganic oxide, inorganic nitride and inorganic nitridedoxide.

The nineteenth aspect: The process according to the fifteenth aspect,wherein said release agent layer is made of at least one materialselected from the group consisting of silicone resin, fluorine resin,polypropylene resin, silicone oil, inorganic oxide, inorganic nitrideand inorganic nitrided oxide.

The twentieth aspect: A semiconductor package obtained by forming bumpsonto a semiconductor wafer serving as said circuit substrate byperformance of the process according to any one of the fourteenth to thenineteenth aspects, followed by dividing said semiconductor wafer intopieces.

The twenty-first aspect: A composition comprising a curing agent, a baserein, a curing promoter, metal particles and a convection additivewherein

the metal particles are dispersed in a mixture of said curing agent andthe base resin, and said convection additive is contained in saidmixture of said curing agent and the base resin;

said curing promoter is contained in an interior of at least one of saidmetal particles, wherein said metal particles melt upon heating so thatsaid curing promoter comes in contact with said mixture to promote acuring reaction between said curing agent and said base resin; and

said convection additive is capable of generating a gas upon heating.

INDUSTRIAL APPLICABILITY

When an electronic component (e.g., semiconductor chip) is mounted overa circuit substrate, a metal particles-dispersed composition of thepresent invention allows the solder material and the like toself-assemble into a region between the opposed electrodes prior to aninitiation of the curing reaction. As a result, there is no residualsolder material that is left outside of the region between the opposedelectrodes, which will lead to an improvement of electrical insulatingproperties. Therefore, the metal particles-dispersed composition of thepresent invention is particularly useful for an flip chip mounting fieldin which an electronic component and a circuit substrate areinterconnected.

CROSS REFERENCE TO RELATED PATENT APPLICATION

The present application claims the right of priority of Japanese PatentApplication No. 2005-065243 (filed on Mar. 9, 2005, the title of theinvention: “METAL PARTICLES-DISPERSED COMPOSITION AND FILP-CHIP MOUNTINGPROCESS AND BUMP-FORMING PROCESS USING THE SAME”), the disclosure ofwhich is incorporated herein by reference.

1. A composition comprising a first component, a second component, metalparticles and a convection additive wherein said metal particles aredispersed in said second component, and said convection additive iscontained in said second component; said first component is contained inan interior of at least one of said metal particles, wherein said metalparticles melt upon heating so that said first component comes incontact with said second component to form a thermoset resin; and saidconvection additive is capable of generating a gas upon heating.
 2. Thecomposition according to claim 1, wherein said first component is acuring agent or a curing promoter used for forming said thermoset resin,whereas said second component is a base resin used for forming saidthermoset resin.
 3. The composition according to claim 2, wherein saidcuring agent is at least one material selected from the group consistingof aliphatic amine, aromatic amine, aliphatic acid anhydride,cycloaliphatic acid anhydride, organic peroxide and polybasic acid; andsaid base resin is at least one material selected from the groupconsisting of epoxy resin, unsaturated polyester resin, alkyd resin,polybutadiene resin, polyimide resin, polyamide resin and cyanate resin.4. The composition according to claim 1, wherein a metal componentconstituting said metal particles is at least one alloy selected fromthe group consisting of Sn—Pb alloy, Sn—Ag alloy, Sn—Ag—Cu alloy,Sn—Bi—Ag—In alloy, Sn—Bi—Zn alloy, Sn—Bi—Ag—Cu alloy, Sn—Zn alloy andSn—Sb alloy.
 5. The composition according to claim 1, wherein saidconvection additive is at least one material selected from the groupconsisting of xylene, isobutyl alcohol, isopentyl alcohol, butylacetate, tetrachlorethylene, methyl isobutyl ketone, ethyl carbitol,butyl carbitol, ethylene glycol, aluminum hydroxide, dawsonite, ammoniummetaborate, barium metaborate and sodium hydrogen carbonate.
 6. Thecomposition according to claim 1, wherein said gas provides a convectioneffect in said composition.
 7. The composition according to claim 1,wherein said composition is in paste form or in sheet form.
 8. Thecomposition according to claim 1, wherein a content of a metal componentconstituting said metal particles ranges from 0.5 to 30% by volume withrespect to said composition.
 9. The composition according to claim 1,wherein a melting point of a metal component constituting said metalparticles is between a curing reaction-initiating temperature and a peaktemperature of the curing reaction with respect to a mixture of saidfirst component and said second component.
 10. The composition accordingto claim 1, wherein a boiling point of said convection additive isbetween a curing reaction-initiating temperature and a peak temperatureof the curing reaction with respect to a mixture of said first componentand said second component, or said convection additive is decomposed togenerate a gas under a temperature condition between a curingreaction-initiating temperature and a peak temperature of the curingreaction.